A New Eye in the Sky (Part 1)

The James Webb Space Telescope (JWST) has released the first of its “operational” images—ones that do actual science instead of ones involved with necessary alignment of the optics. What do they show us?

First, let’s do a brief overview of the telescope itself. There is a more detailed description here, but we’ll focus on the images for the bulk of this post.

How does JWST compare to the Hubble Space Telescope (HST), the marvelous instrument that brought us so many iconic images? First, JWST is BIG.

A telescope’s function is to gather light, which contains information about the object being viewed. More light equals more information. Think of a telescope as a light bucket. The bigger the bucket, the more light—and the more information.

Next, it is sensitive to a different region of the electromagnetic spectrum, to the longer wavelengths of light called infrared (IR), light that is invisible to human eyes. It is also invisible to the HST, and to any ground-based telescopes. Earth’s atmosphere blocks all but a few wavelengths of infrared light.

This not only allows JWST to see wavelengths that HST cannot. JWST can see THROUGH clouds of gas and dust that block visible light. Cameras sensitive to IR allow firefighters to see potential fire victims even in the smokiest environments.

One more thing. If IR light is invisible to us, how can we see anything in these images? The colors shown here have been shifted from their original invisible IR to wavelengths in the visible region. Objects that are red are emitting in the far IR, the longest wavelengths. Bluer objects emit in still invisible but shorter IR wavelengths.

So let’s take a look at two of the five images.

LOOKING OUT IS LOOKING BACK.

This video shows the same tiny patch of sky as seen by JWST and HST. The JWST image is filled with galaxies!

Why so many more galaxies in the JWST image?

The galaxies that appear in both images show the combined light from billions or even trillions of stars. All stars emit light across the electromagnetic spectrum. The Hubble Space Telescope can see light in visible and ultraviolet wavelengths, and that’s what appears in its images.

JWST sees in infrared. Galaxies that are especially far away from us have had their light stretched to longer wavelengths by the expansion of the universe. The most distant ones have had the visible and ultraviolet light they emit stretched into the infrared. This makes them invisible to the Hubble, but JWST can see them.

It can also see the galaxies that Hubble saw, because the nearby galaxies, in addition to emitting in the visible and ultraviolet, ALSO emit in infrared. JWST has ADDED galaxies that were invisible to Hubble.

Those added galaxies, with their light stretched to far IR wavelengths, are the most distant and the ones whose light comes to us from the earliest epochs of the universe’s 13.8 billion year history. JWST is a time machine that lets us see farther back than ever before, back to when the first stars and galaxies were forming after the Big Bang.

PEERING INSIDE A PLANETARY NEBULA

A planetary nebula (so called because their round shape looked like a planet in the small telescopes of early astronomers) is a shell of gas and dust emitted by a dying star. As you might suspect, the interior of these shells, and their fine structure, are largely invisible to Hubble. This is Hubble’s view of the Southern Ring Nebula.

The two images below are from two different instruments on JWST, looking at the Southern Ring Nebula in two different IR wavelengths.

There are actually two stars at the center of the nebula, orbiting each other and stirring up the gas and dust shell into complex patterns. The brighter of the two, the only one visible in the left hand image, is not the one responsible for emitting these materials. The dimmer star visible in the right hand image is the culprit!

Also note the streak of light at the ten o’clock position. It is a beam of starlight poking through a hole in the shell, just like sunlight beaming through a gap in a cloud.

We’ll take a look at the other images released in a subsequent post. Stay tuned!